Vacuum cleaner with motor cooling

ABSTRACT

A vacuum cleaner having a dirt-separation stage and a vacuum motor for moving air through the dirt-separation stage. The vacuum motor includes an impeller driven by an electric motor. The impeller is then located upstream of the dirt-separation stage, the electric motor is located downstream of the dirt-separation stage, and at least part of the air discharged from the dirt-separation stage is used to cool the electric motor.

REFERENCE TO RELATED APPLICATION

This application claims priority of United Kingdom Application No.1418795.9, filed Oct. 22, 2014, the entire contents of which areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to a vacuum cleaner having a motor that iscooled by air discharged from a dirt-separation stage.

BACKGROUND OF THE INVENTION

A vacuum cleaner typically comprises a vacuum motor that pullsdirt-laden air through one or more dirt-separation stages. Thedirt-separation stages are typically located upstream of the vacuummotor in order to protect the vacuum motor from the dirt carried by theair. After passing through the dirt-separation stages, the cleansed airmay be drawn through the interior of the vacuum motor in order to coolthe motor.

SUMMARY OF THE INVENTION

The present invention provides a vacuum cleaner comprising adirt-separation stage and a vacuum motor for moving air through thedirt-separation stage, wherein the vacuum motor comprises an impellerdriven by an electric motor, the impeller is located upstream of thedirt-separation stage, the electric motor is located downstream of thedirt-separation stage, and at least part of the air discharged from thedirt-separation stage is used to cool the electric motor.

As air is drawn through the vacuum cleaner, there is a pressure dropacross the dirt-separation stage. In contrast to a conventional vacuumcleaner, the dirt-separation stage is located downstream rather thanupstream of the impeller. As a result, the air pressure at the inlet ofthe impeller is higher. Since the air pressure at the inlet is higher,the impeller imparts a greater pressure rise to the air. This greaterpressure rise may then be used to increase the flow rate, increase theseparation efficiency and/or decrease the power consumption of thevacuum cleaner.

At least part of the air discharged from the dirt-separation stage isused to cool the vacuum motor. As a result, the vacuum motor may operateat higher electrical power.

At least part of the air discharged from the dirt-separation stage maybe pushed through the interior of the vacuum motor so as to cool theelectric motor. If the vacuum cleaner as a whole were located upstreamof the dirt-separation stage and if the air drawn into the vacuum motorwere used to cool the electric motor, the dirt carried by the air maydamage or otherwise shorten the lifespan of the electric motor. Forexample, the dirt may clog bearings or cover thermally-sensitiveelectrical components. By locating the dirt-separation stage downstreamof the impeller but upstream of the electric motor, the advantagesoutlined above may be achieved whilst simultaneously cooling theelectric motor using relatively clean air.

The air pushed through the interior of the vacuum motor may be used tocool one or more components of the electric motor. In particular, theair may flow over and cool an electrical winding and/or a power switchfor controlling current in the winding. As a result, the winding andpower switch are able to carry higher currents and thus the electricmotor is able to operate at higher electrical power.

The vacuum motor may comprise a first inlet, a first outlet, a secondinlet and a second outlet. The first inlet is then located upstream ofthe impeller, whilst the first outlet is located downstream of theimpeller and upstream of the dirt-separation stage. The second inlet isthen located downstream of the dirt-separation stage, whilst the secondoutlet is located downstream of the second inlet. At least part of theair discharged from the dirt-separation stage then enters the vacuummotor via the second inlet, flows over one or more components of theelectric motor and exits the vacuum motor via the second outlet.

The dirt-separation stage may comprise a cyclonic separator. This thenhas the advantage that dirt may be removed from the air without the needfor a filter or other means that requires washing or replacing.

The dirt-separation stage may comprise a plurality of cyclonicseparators arranged around the vacuum motor. By employing a plurality ofcyclonic separators, a relatively high separation efficiency may beachieved for the dirt separation stage. By arranging the cyclonicseparators around the vacuum motor, a relatively short and/or straightpath may be taken between the outlet of the vacuum motor and the inletof each of the cyclonic separators. As a result, relatively high speedsmay be achieved for the air entering the cyclonic separators, therebyimproving the separation efficiency.

The dirt-separation stage may comprise a plurality of channels, eachchannel extending from an outlet of the vacuum motor to an inlet of arespective cyclonic separator. The channels may then be used to avoidabrupt changes in the speed of the air as it moves from the vacuum motorto the cyclonic separators, thereby reducing flow losses. In particular,the channels may be used to ensure that the relatively high speed of theair exiting the vacuum motor is largely maintained on entering thecyclonic separators.

The inlet angle of each channel may be defined so as to minimise theincidence angle of the air entering the channel during normal use of thevacuum cleaner. As a result, flow losses are reduced. The absolute flowangle at which the air exits the impeller may be in excess of 30degrees. Accordingly, each channel may have an inlet angle of at least30 degrees.

Each channel may be substantially straight. Consequently there is no orrelatively little turning of the air as it moves along the channel Bycontrast, if the air were forced to follow a tortuous path between thevacuum motor and the cyclonic separators, flow losses would be greaterand thus the speed of the air entering the cyclonic separators would beslower.

The impeller may be a centrifugal impeller, which has the advantage ofbeing able to achieve relatively high flow rates in relation to itssize. Air then enters the vacuum motor in an axial direction (i.e. in adirection parallel to the rotational axis of the vacuum motor), andexits in a radial direction (i.e. in a direction normal to therotational axis of the vacuum motor). Since the air exits in a radialdirection, it is not necessary to turn the air exiting the impeller andthus flow losses are reduced. Furthermore, where the dirt-separationstage comprises a plurality of cyclonic separators arranged around thevacuum motor, a relatively straight path may be established between theoutlet of the vacuum motor and the inlet to each of the cyclonicseparators, thereby further reducing losses.

The vacuum cleaner may comprise a further dirt-separation stage, and theimpeller may be located downstream of the further dirt separation stage.The further dirt-separation stage may then be used to remove dirt thatwould otherwise block, jam or damage the impeller. For example, thefurther dirt-separation stage may be used to remove relatively coarsedirt, whilst the dirt-separation stage may be used to remove relativelyfine dirt from the air.

The further dirt-separation stage may comprise a cyclonic separator.Dirt that might otherwise black, jam or damage the impeller may then beremoved without the need for a filter or other means that would requirewashing or replacing.

Where the first dirt-separation stage comprises a cyclonic separator,the cyclonic separator may have a central axis about which air withinthe cyclonic separator rotates. The vacuum motor may then comprise arotational axis about which the impeller rotates, and the central axisand the rotational axis may be coincident. As a consequence, arelatively straight path may then be taken by the air as it moves fromthe further dirt-separation stage to the vacuum motor, thus reducingflow losses.

The dirt-separation stage may comprise a dirt collector, the furtherdirt-separation stage may comprise a further dirt collector, and thefurther dirt collector may surround the dirt collector. As a result, arelatively compact arrangement may be realised. The furtherdirt-separation stage may be used to remove relatively coarse dirtwhilst the dirt-separation stage may be used to remove relatively finedirt. Since the further dirt collector surrounds the dirt collector, arelatively large volume may be achieved for the further dirt collectorwhilst maintaining a relatively compact overall size.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present invention may be more readily understood, anembodiment of the invention will now be described, by way of example,with reference to the accompanying drawings, in which:

FIG. 1 is a perspective view of a vacuum cleaner in accordance with thepresent invention;

FIG. 2 is a sectional slice through the centre of a dirt separator ofthe vacuum cleaner, the sectional slice being taken in the verticalplane;

FIG. 3 is an enlarged view of the upper portion of the sectional sliceof FIG. 2;

FIG. 4 is a sectional slice through the dirt separator, the sectionalslice being taken in the horizontal plane indicated by the line X-X inFIG. 3;

FIG. 5 illustrates the inlet angle (a) of a channel of the dirtseparator, the absolute flow angle (β) of the airflow entering thechannel, and the resulting incidence angle (γ);

FIG. 6 is a perspective view of a vacuum motor forming part of the dirtseparator; and

FIG. 7 is an exploded view of the vacuum motor along with a pair ofmounts used to mount the vacuum motor.

DETAILED DESCRIPTION OF THE INVENTION

The vacuum cleaner 1 of FIG. 1 comprises a main body 2 to which a dirtseparator 3 is removably attached.

Referring now to FIGS. 2 to 7, the dirt separator 3 comprises a firstdirt-separation stage 4, a motor plenum 5, a vacuum motor 6, and asecond dirt-separation stage 7.

The first dirt-separation stage 4 comprises a cyclonic separator 10 anda dirt collector 11. The cyclonic separator 10 and the dirt collector 11are defined by an outer wall 12, an inner wall 13, a shroud 14, and abase 15. The outer wall 12 is cylindrical in shape and surrounds theinner wall 13 and the shroud 14. The inner wall 13 is generallycylindrical in shape and is arranged concentrically with the outer wall12. The upper part of the inner wall 13 is fluted, with the flutesproviding passageways along which dirt separated by the cyclonicseparators 40 of the second dirt-separation stage 7 are guided to afurther dirt collector 42. The shroud 14 is located between the outerwall 12 and the inner wall 13 and comprises a mesh through which air ispermitted to pass.

The upper end of the outer wall 12 is closed off by a wall of the seconddirt-separation stage 7. The lower ends of the outer wall 12 and theinner wall 13 are closed off by the base 15. The outer wall 12, theinner wall 13, the shroud 14 and the base 15 thus collectively define achamber. The upper part of this chamber (i.e. that part generallydefined between the outer wall 12 and the shroud 14) defines a cyclonechamber 16, whilst the lower part of the chamber (i.e. that partgenerally defined between the outer wall 12 and the inner wall 13)defines a dirt-collection chamber 17. The first dirt-separation stage 4therefore comprises a cyclonic separator 10 and a dirt collector 11located below the cyclonic separator 10.

The outer wall 12 includes an opening (not shown) that serves as aninlet to the first dirt-separation stage 4. The space between the shroud14 and the inner wall 13 defines a passageway 18 that is closed at alower end and is open at an upper end. The upper end then serves anoutlet for the first dirt-separation stage 4.

The motor plenum 5 is located above the first dirt-separation stage 4and serves to connect fluidly the outlet of first-dirt separation stage4 with the inlet of the vacuum motor 6.

The vacuum motor 6 comprises a housing 20, an impeller 21, and anelectric motor 22. The impeller 21 is a centrifugal impeller that isdriven by the electric motor 22. The housing 20 is generally cylindricalin shape, is closed at a front end and is open at a rear end. Theimpeller 21 and the electric motor 22 are then housed within the housing20 such that the impeller 21 is adjacent the front end.

The housing 20 comprises a first inlet 25 located upstream of theimpeller 21, a first outlet 26 located downstream of the impeller 21, asecond inlet 27 located downstream of the first outlet 26, and a secondoutlet 28 located downstream of the second inlet 27. The first inlet 25comprises a circular opening located in the front end of the housing 20.The first outlet 26 comprises an annular opening formed around the sideof the housing 20. The second inlet 27 comprises a plurality ofapertures that are again formed around the side of the housing 20. Thesecond inlet 27 is located rearward of the first outlet 26, which is tosay that, relative to the first outlet 26, the second inlet 27 islocated further towards the rear of the housing 20. Finally, the secondoutlet 28 comprises a plurality of apertures that are defined betweenthe open rear end of the housing 20 and the electric motor 22.

The first inlet 25 is aligned with the inlet of the impeller 21, whilstthe first outlet 26 is aligned with and surrounds the outlet of theimpeller 21. In being a centrifugal impeller, air enters the impeller 21in an axial direction (i.e. in a direction parallel to the rotationalaxis) and exists in a radial direction (i.e. in a direction normal tothe rotational axis). Consequently, air enters the vacuum motor 6 viathe first inlet 25 in an axial direction, and exits the vacuum motor 6via the first outlet 26 in a radial direction. As explained below, airdischarged from the second dirt-separation stage 7 re-enters the vacuummotor 6 via the second inlet 27, flows over and cools components of theelectric motor 22, and exits via the second outlet 28.

The vacuum motor 6 is mounted within the second dirt-separation stage 7by means of an axial mount 29 and a radial mount 30. Both mounts 29,30are formed of an elastomeric material and act to isolate the seconddirt-separation stage 7 and thus the remainder of the dirt separator 3from the vibration generated by the vacuum motor 6. The axial mount 29is attached to the front end of the housing 20 and abuts a wall of thesecond dirt-separation stage 7 so as to form a seal. During use, theaxial mount 29 deforms to absorb vibration of the vacuum motor 6 in anaxial direction, i.e. in a direction parallel to the axis of rotation ofthe vacuum motor 6. The radial mount 30 is attached to the side of thehousing 20 and comprises a sleeve 31 that surrounds the housing 20, alip seal 32 located at one end of the sleeve 31, and a plurality of ribs33 that extend axially along the sleeve 31. The radial mount 30 abuts awall of the second dirt-separation stage 7 such that the lip seal 32forms a seals against the wall, whilst the ribs 33 are crushed slightly.During use, the ribs 33 further deform to absorb vibration of the vacuummotor 6 in a radial direction, i.e. in a direction normal to the axis ofrotation of the vacuum motor 6.

The second dirt-separator stage 7 comprises a plurality of cyclonicseparators 40, a plurality of channels 41, a dirt collector 42, and acover 43.

The cyclonic separators 40 are arranged in a ring about the vacuum motor6. Each cyclonic separator 40 is frusto-conical in shape and comprises atangential inlet 44, an air outlet 45, and a dirt outlet 46. Theinterior of each cyclonic separator 40 defines a cyclone chamber 47.During use, air enters the cyclone chamber 47 via the tangential inlet44. Dirt separated within the cyclone chamber 47 is then dischargedthrough the dirt outlet 46 whilst the cleansed air exits through the airoutlet 45.

Each channel 41 extends linearly from the first outlet 26 of the vacuummotor 6 to the inlet 44 of a respective cyclonic separator 40. Thecyclonic separators 40 are positioned relative to the vacuum motor 6such that the inlet 44 of each cyclonic separator 40 is located roughlyat the same level as the first outlet 26. The height of each inlet 44 isgreater than the height of the first outlet 26. Accordingly, eachchannel 41 increases in height as it extends from the first outlet 26 tothe inlet 44. Additionally, the channel 41 decreases in width as itextends between the first outlet 26 and the inlet 44. This then ensuresthat the cross-sectional area of the channel 41 is relatively constantalong its length, the advantages of which are explained below.

As illustrated in FIG. 4, each channel 41 has a centreline 50 thatextends from the inlet to the outlet of the channel 41. Each channel 41then has an inlet angle α defined by the intersection of (i) the tangentto the centreline 50 at the inlet of the channel 41, and (ii) the radialaxis 51 of the impeller 21 extending through the centre of the inlet ofthe channel 41. The term ‘inlet angle’ is therefore used in the samemanner as that employed in compressor technology when referring to theblades or vanes of a diffuser. For example, the inlet angle of adiffuser vane is defined as the angle between (i) the tangent to thecamber line at the leading edge of the vane, and (ii) the radial axis ofthe impeller extending through the leading edge of the vane. Thechannels 41 of the second dirt-separation stage 7 resemble a channeldiffuser. However, in contrast to a conventional channel diffuser, whichseeks to decelerate the airflow in order to increase the staticpressure, the channels 41 of the second dirt-separation stage 7 does notattempt to decelerate the airflow; the reasons for this are set outbelow.

Referring now to FIG. 5, the inlet angle α of each channel 41 is definedso as to minimise the incidence angle γ of the airflow. During normaluse of the vacuum cleaner 1, the flow rate of the airflow passingthrough the cyclonic separator 3 will vary, e.g. as the vacuum cleaner 1is used on different surfaces. As the flow rate varies, so too does theabsolute flow angle β of the airflow exiting the impeller 21. Forexample, the flow rate may vary between 5 l/s and 15 l/s. At the lowerflow rate, the vacuum motor 6 rotates at a higher speed due to thereduced load and thus the airflow exits the impeller 21 at a higher flowangle of, say, 65 degrees. At the upper flow rate, the vacuum motor 6rotates at a lower speed due to the increased load and thus the airflowexits the impeller 21 at a lower flow angle of, say, 35 degrees. Theaverage flow rate during normal use may be, say, 10 l/s resulting in anabsolute flow angle of 50 degrees. The inlet angle α of each channel istherefore defined as 50 degrees so as to minimise the incidence angle γ.

The dirt collector 42 is defined by the inner wall 13 and the base 15.More particularly, the interior space bounded by the inner wall 13 andthe base 15 defines a dirt-collection chamber 48. The dirt collectors11,42 of the two dirt-separation stages 4,7 are therefore adjacent.Moreover, the dirt collector 11 of the first dirt-separation stage 4surrounds the dirt collector 42 of the second dirt-separation stage 7.As explained below, the first dirt-separation stage 4 is intended toremove relatively coarse dirt, whilst the second dirt-separation stage 7is intended to remove relatively fine dirt. By having a first dirtcollector 11 that is outermost and surrounds a second dirt collector 42,a relatively large volume may be achieved for the first dirt collector11 whilst achieving a relatively compact overall size for the dirtseparator 3.

The bottom of each cyclonic separator 40 projects into the dirtcollector 42 such that dirt separated by the cyclonic separator 40 isdischarged through the dirt outlet 46 and falls into the dirt-collectionchamber 48. As noted above, the upper part of the inner wall 13 isfluted. The flutes provide passageways along which the dirt separated bythe cyclonic separators 40 is guided to the bottom of thedirt-collection chamber 48.

The cover 43 overlies the cyclonic separators 40 and the vacuum motor 6.The cover 43 acts to guide the cleansed air discharged from the cyclonicseparators 40 to the second inlet 27 of the vacuum motor 6. The lip seal32 of the radial mount 30 forms an annular seal against the cover 43such that all air discharged from the cyclonic separators 40 re-entersthe vacuum motor 6 via the second inlet 27. The cover 43 comprises aplurality of exhaust vents 49 located above the vacuum motor 6. Airdischarged from the vacuum motor 6 via the second outlet 28 is thenexhausted from the dirt separator 3 and the vacuum cleaner 1 via theexhaust vents 49.

During use, the vacuum motor 6 pulls dirt-laden air in through a suctioninlet of the vacuum cleaner 1. The dirt-laden air is then carried viaducting from the suction inlet to the dirt separator 3. The dirt-ladenair enters the first dirt-separation stage 4 via the inlet in the outerwall 12. The dirt-laden air then spins within the cyclone chamber 16causing relatively coarse dirt to be separated. The coarse dirt collectsin the dirt-collection chamber 17, whilst the partially cleansed air ispulled through the shroud 14, up through the passageway 18, and into themotor plenum 5. From the motor plenum 5, the partially cleansed air ispulled into the vacuum motor 6 via the first inlet 25. The air is thendischarged from the vacuum motor 6 via the first outlet 26. Thepartially cleansed air is then pushed along the channels 41 of thesecond dirt-separation stage 7 and into the cyclonic separators 40 viathe tangential inlets 44. The partially cleansed air then spins withinthe cyclone chambers 47 causing relatively fine dirt to be separated.The fine dirt is discharged through the dirt outlet 46 and collects inthe dirt-collection chamber 48, whilst the cleansed air is dischargedthrough the air outlet 45. From there, the cleansed fluid is pushed intothe vacuum motor 6 via the second inlet 27. The cleansed air is thenpushed through the interior of the vacuum motor 6 causing components ofthe electric motor 22 to be cooled. Finally, the cleansed, heated air isdischarged from the vacuum motor 6 via the second outlet 28 and isexhausted from the vacuum cleaner 1 via the exhaust vents 49 in thecover 43.

The first dirt-separation stage 4 is located upstream of the impeller21, whilst the second dirt-separation stage 7 is located downstream ofthe impeller 21. Consequently, air is pulled through the firstdirt-separation stage 4 but is pushed through the second dirt separationstage 7. This arrangement contrasts with a conventional vacuum cleanerin which both dirt-separation stages are located upstream of the vacuummotor. As air passes through a dirt-separation stage, there is apressure drop in the airflow. Since the second dirt-separation stage 7is located downstream of the impeller 21, the pressure drop associatedwith the second dirt-separation stage 7 occurs downstream of theimpeller 21. As a result, the pressure at the inlet of the impeller 21is higher in comparison to a conventional arrangement in which bothdirt-separation stages are located upstream of the impeller.Consequently, for the same shaft power generated by the electric motor22, a greater pressure rise is imparted to the air by the impeller 21.This greater pressure rise may then be used to increase the flow rate,increase the separation efficiency and/or decrease the power consumptionof the vacuum cleaner 1, as will now be explained.

If the shaft power of the electric motor 22 and the separationefficiencies of the dirt-separation stages 4,7 are unchanged, thegreater pressure rise generated by the impeller 21 will result in ahigher flow rate through the vacuum cleaner 1. As a result, greatersuction power will be generated at the suction inlet of the vacuumcleaner 1. Rather than increasing the flow rate, the greater pressurerise generated by the impeller 21 may instead be used to increase theseparation efficiency of one or both of the dirt-separation stages 4,7.As the separation efficiency of a dirt-separation stage increases, sotoo does the pressure drop associated with the stage. Accordingly, thegreater pressure rise may be used to increase the separation efficiencyof one or both of the dirt-separation stages 4,7 whilst maintaining thesame flow rate through the vacuum cleaner 1. Finally, rather thanincreasing the flow rate or the separation efficiency, the shaft powerof by the electric motor 22 may be reduced so that the same flow rateand separation efficiency are achieved. As a result, the same cleaningperformance is achieved but at a lower power consumption.

In view of the benefits in locating the second dirt-separation stage 7downstream of the impeller 21, one might be tempted to locate the firstdirt-separation stage 4 downstream of the impeller 21. This would thenfurther increase the pressure at the inlet of the impeller 21. However,locating the first dirt-separation stage 4 downstream of the impeller 21would then expose the impeller 21 to all of the dirt that is drawn intothe vacuum cleaner 1. By locating the first dirt-separation stage 4upstream of the impeller 21, relatively coarse dirt, which mightotherwise block, jam or damage the impeller 21, is first removed fromthe airflow. The impeller 21 is therefore exposed only to relativelyfine dirt carried by the partially cleansed air.

The vacuum motor 6 comprises a centrifugal impeller 21, which has theadvantage of relatively high flow rates in relation to its size. As aconsequence of employing a centrifugal impeller, air enters the impeller21 in an axial direction, and exits in a radial direction. The housing20 includes an outlet 26 that surrounds the outlet of the impeller 21.As a result, it is not necessary to turn the air exiting the impeller 21within the housing 20, thereby reducing flow losses. Additionally, theair exiting the vacuum motor 6 moves at relatively high speed, which aswill now be explained has significant advantages for the separationefficiency of the second dirt-separation stage 7.

The cyclonic separators 40 of the second dirt-separation stage 7 arearranged around the vacuum motor 6. As a result, a relatively short andstraight path is provided for the airflow as it moves from the firstoutlet 26 of the vacuum motor 6 to the inlets 44 of the cyclonicseparators 40. This then helps reduce flow losses that would otherwisearise if the airflow were forced to follow a tortuous path between thevacuum motor 6 and the cyclonic separators 40. The first outlet 26 ofthe vacuum motor 6 is located roughly at the same level as the inlet 44to each cyclonic separator 40. In particular, the first outlet 26 liesin a plane that passes though the inlet 44 of each cyclonic separator40. As a result, there is relatively little turning of the air in anaxial direction, thereby reducing flow losses.

The channels 41 help to ensure that the speed of the air exiting thevacuum motor 6 is maintained at the inlets 44 to the cyclonic separators40. To this end, each channel 41 is straight and has an inlet angle αthat serves to minimise the incidence angle γ of the airflow duringnormal use of the vacuum cleaner 1. Additionally, the cross-sectionalarea of each channel 41 is constant along the length of the channel 41.As a result, the relatively high speed of the air exiting the vacuummotor 6 is largely maintained at the inlets 44 of the cyclonicseparators 40. This then has the advantage of improving the separationefficiency of the cyclonic separators 40.

In a conventional vacuum cleaner having cyclonic separators locatedupstream of a vacuum motor, the air is typically accelerated at theinlets to the cyclonic separators, which act as nozzles for the airflow.The air discharged from the cyclonic separators then flows into aplenum, causing the airflow to decelerate. Finally, the air is againaccelerated at the vacuum motor. The airflow is therefore subjected toabrupt changes in speed as the airflow moves between the cyclonicseparators and the vacuum motor. However, with each abrupt change inspeed, the airflow experiences flow losses. With the vacuum cleaner 1 ofthe present invention, the channels 41 act to prevent abrupt changes inspeed as the airflow moves between the vacuum motor 6 and the cyclonicseparators 40, thereby reducing flow losses.

The cross-sectional area of each channel 41 is constant along itslength. As a result, the speed of the airflow entering the cyclonicseparators 40 is largely the same as that exiting the vacuum motor 6.However, depending on the particular design of the cyclonic separators40 (e.g. size, shape and number) as well as the speed of the airflowexiting the vacuum motor 6, it may be desirable to either accelerate ordecelerate the airflow. Accordingly, the cross-sectional area of eachchannel 41 may decrease or increase gradually along its length.Nevertheless, in contrast to the conventional vacuum cleaner describedin the previous paragraph, the airflow does not undergo an abrupt changein speed on its path from the vacuum motor 6 to the cyclonic separators40.

As noted above, the inlet angle α of each channel 41 is ideally definedso as to minimise the incidence angle α. The inlet angle will thereforedepend on the absolute flow angle β of the airflow exiting the vacuummotor 6, which in turn depends on the design of the impeller 21 and thespeed of rotation of the electric motor 22. Since the vacuum motor 6forms part of the dirt separator 3 and the dirt separator 3 is removablefrom the main body 2, it is desirable to employ a vacuum motor 6 that isrelatively compact and light in weight. In order to achieve a relativelycompact size and light weight whilst achieving the desired flow rate,relatively high speeds of rotation are likely. Accordingly, the absoluteflow angle at which the air exits the impeller 21 is likely to be inexcess of 30 degrees. Each channel 41 would then have an inlet angle αof at least 30 degrees.

The vacuum motor 6 is located directly above the first dirt-separationstage 4. Additionally, the central axis of the cyclonic separator 10(i.e. the axis about which air rotates within the cyclone chamber 16)and the rotational axis of the vacuum motor 6 are coincident. As aresult, a relatively short and straight path is taken by the air as itmoves from the first dirt-separation stage 4 to the vacuum motor 6,thereby reducing flow losses.

The two dirt-separation stages 4,7 form part of a common dirt separator3 that is removable from the main body 2. This then has the advantagethat the dirt separator 3 may be removed, carried to a bin and the dirtcollected by both separation stages 4,7 may be emptied together in asingle action. For example, the base 15 may pivot relative to the outerwall 12 in order to empty both dirt-collection chambers 17,48. Thevacuum motor 6 also forms part of the dirt separator 3. Whilst this hasthe disadvantage of increasing the size and weight of the dirt separator3, it has the advantage that a shorter and less tortuous path is takenby the air when moving from the first dirt-separation stage 4 to thevacuum motor 6 and when moving from the vacuum motor 6 to the seconddirt-separation stage 7. As a result, flow losses are reduced.

The first dirt-separation stage 4 comprises a cyclonic separator 10,which has the advantage that relatively coarse dirt may be removedwithout the need for a filter or other means that would require washingor replacing. Nevertheless, the first dirt-separation stage 4 maycomprise alternative means, such as a washable filter, for removing dirtthat would otherwise block, jam or damage the impeller 21.

The cleansed air discharged from the second dirt-separation stage 7 ispushed through the interior of the vacuum motor 6 and is used to coolcomponents of the electric motor 22. In particular, the cleansed airflows over and cools electrical windings 34 and power switches 35 thatare used to control the flow of current through the windings 34. As aresult, the electric motor 22 is able to operate at higher electricalpower. If the vacuum cleaner 6 as a whole were located upstream of thesecond dirt-separation stage 7 and if the air drawn through the vacuummotor 6 were used to cool the electric motor 22, the fine dirt carriedby the airflow may damage or otherwise shorten the lifespan of theelectric motor 22. For example, the dirt may clog bearings or coverthermally-sensitive electrical components. By locating the seconddirt-separation stage 7 downstream of the impeller 21 but upstream ofthe electric motor 22, the advantages outlined above regarding a greaterpressure rise may be achieved whilst simultaneously cooling the electricmotor 22 using relatively clean air.

All of the air discharged from the second dirt-separation stage 7 ispushed through the interior of the vacuum motor 6. This then has theadvantage of maximising cooling since all of the available air isreturned through the vacuum motor 6. Nevertheless, the path through thevacuum motor 6 may be relatively restrictive. It may therefore bedesirable to push only a part of the airflow through the vacuum motor 6.The remainder of the airflow would then bypass the second inlet 27 andinstead flow along the outside of the vacuum motor 6. This may beachieved, for example, by adapting the radial mount 30 such that the lipseal 32 forms only a partial seal. By pushing only part of the airflowthrough the interior of the vacuum motor 6, the flow rate shouldincrease owing to the less restrictive path formed by the bypass. Ifcooling of the electric motor 22 is not a concern or can be achieved byother means, pushing the air from the second dirt-separation stage 7through the interior of the vacuum motor 6 may be avoided altogether.Alternatively, if the housing 20 is made of metal or some other materialhaving a high thermal conductivity then it may be possible to achievesufficient cooling of the electric motor 22 by passing the air along theoutside of the vacuum motor 6.

1. A vacuum cleaner comprising a dirt-separation stage and a vacuummotor for moving air through the dirt-separation stage, wherein thevacuum motor comprises an impeller driven by an electric motor, theimpeller is located upstream of the dirt-separation stage, the electricmotor is located downstream of the dirt-separation stage, and at leastpart of the air discharged from the dirt-separation stage is used tocool the electric motor.
 2. The vacuum cleaner of claim 1, wherein atleast part of the air discharged from the second dirt-separation stageis pushed through the interior of the vacuum motor so as to cool theelectric motor.
 3. The vacuum cleaner of claim 2, wherein the air pushedthrough the interior of the vacuum motor flow over and cools at leastone of an electrical winding and a power switch for controlling currentin the electrical winding.
 4. The vacuum cleaner of claim 1, wherein thevacuum motor has a first inlet, a first outlet, a second inlet and asecond outlet, the first inlet is located upstream of the impeller, thefirst outlet is located downstream of the impeller and upstream of thedirt-separation stage, the second inlet is located downstream of thedirt-separation stage, the second outlet is located downstream of thesecond inlet, and at least part of the air discharged from thedirt-separation stage enters the vacuum motor via the second inlet,flows over one or more components of the electric motor and exits thevacuum motor via the second outlet.
 5. The vacuum cleaner of claim 1,wherein the dirt-separation stage comprises a cyclonic separator.
 6. Thevacuum cleaner of claim 1, wherein the dirt-separation stage comprises aplurality of cyclonic separators arranged around the vacuum motor. 7.The vacuum cleaner of claim 6, wherein the dirt-separation stagecomprises a plurality of channels, each channel extending from an outletof the vacuum motor to an inlet of a respective cyclonic separator. 8.The vacuum cleaner of claim 7, wherein each channel has an inlet angleof at least 30 degrees.
 9. The vacuum cleaner of claim 7, wherein eachchannel is substantially straight.
 10. The vacuum cleaner of claim 1,wherein the vacuum cleaner comprises a further dirt-separation stage,and the impeller is located downstream of the further dirt separationstage.
 11. The vacuum cleaner of claim 10, wherein the furtherdirt-separation stage comprises a cyclonic separator.
 12. The vacuumcleaner of claim 11, wherein the cyclonic separator of the firstdirt-separation stage comprises a central axis about which air withinthe cyclonic separator rotates, the vacuum motor comprises a rotationalaxis about which the impeller rotates, and the central axis and therotational axis are coincident.
 13. The vacuum cleaner of claim 10,wherein the dirt-separation stage comprises a dirt collector, thefurther dirt-separation stage comprises a further dirt collector, andthe further dirt collector surrounds the dirt collector.